It is such a large business decision to move to either package, that I would say the $s are going to be significant.
The decision for even a smallish company might be well worth looking at a consultant to help you work through things.
In addition to what others have noted here, you also want to consider where new hires will come from. If your geographical area has a very large population of designers who work with ProE (for example), and all else is equal, you may be better able to get contract work or new hires from that pool of workers, or the other way around if it is SolidWorks.
Issues of document management with both packages will be critical, and so will be the training time and cost.
Then will likely come some conversion of legacy paper data for reuse, spares & repairs, etc, whether done in house or jobbed out to local guys on a contract basis.
Bo